LM2991 Negative Low Dropout Adjustable Regulator

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1 LM2991 Negative Low Dropout Adjustable Regulator General Description The LM2991 is a low dropout adjustable negative regulator with a output voltage range between 3V to 24V. The LM2991 provides up to 1A of load current and features a On /Off pin for remote shutdown capability. The LM2991 uses new circuit design techniques to provide a low dropout voltage, low quiescent current and low temperature coefficient precision reference. The dropout voltage at 1A load current is typically 0.6V and a guaranteed worst-case maximum of 1V over the entire operating temperature range. The quiescent current is typically 1 ma with a 1A load current and an input-output voltage differential greater than 3V. A unique circuit design of the internal bias supply limits the quiescent current to only 9 ma (typical) when the regulator is in the dropout mode (V OUT V IN 3V). The LM2991 is short-circuit proof, and thermal shutdown includes hysteresis to enhance the reliability of the device when inadvertently overloaded for extended periods. The LM2991 is available in 5-lead TO-220 and TO-263 packages and is rated for operation over the automotive temperature range of 40 C to +125 C. Mil-Aero versions are also available. Typical Application Features n Output voltage adjustable from 3V to 24V, typically 2V to 25V n Output current in excess of 1A n Dropout voltage typically 0.6V at 1A load n Low quiescent current n Internal short circuit current limit n Internal thermal shutdown with hysteresis n TTL, CMOS compatible ON/OFF switch n Functional complement to the LM2941 series Applications n Post switcher regulator n Local, on-card, regulation n Battery operated equipment May 1999 LM2991 Negative Low Dropout Adjustable Regulator DS V OUT = V REF (1 + R2/R1) *Required if the regulator is located further than 6 inches from the power supply filter capacitors. A 1 µf solid tantalum or a 10 µf aluminum electrolytic capacitor is recommended. **Required for stability. Must be at least a 10 µf aluminum electrolytic or a 1 µf solid tantalum to maintain stability. May be increased without bound to maintain regulation during transients. Locate the capacitor as close as possible to the regulator. The equivalent series resistance (ESR) is critical, and should be less than 10Ω over the same operating temperature range as the regulator National Semiconductor Corporation DS

2 Connection Diagrams and Ordering Information 5-Lead TO-220 Straight Leads 5-Lead TO-220 Bent, Staggered Leads DS Front View Order Number LM2991T See NS Package Number T05A DS Front View Order Number LM2991T Flow LB03 See NS Package Number T05D TO263 5-Lead Surface-Mount Package Top View DS DS Side View Order Number LM2991S See NS Package Number TS5B 16-Lead Ceramic Dual-in-Line Package 16-Lead Ceramic Surface-Mount Package DS Top View Order Number LM2991J-QMLV VEA Order Number LM2991J-QML QEA See NS Package Number J16A DS Top View Order Number LM2991WG-QML QXA See NS Package Number WG16A 2

3 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Storage Temperature Range Lead Temperature (Soldering, 10 sec.) Operating Ratings (Note 1) 65 C to +150 C 230 C Input Voltage ESD Susceptibility (Note 2) Power Dissipation (Note 3) Junction Temperature (T Jmax ) 26V to +0.3V 2 kv Internally limited 125 C Junction Temperature Range (T J ) Maximum Input Voltage (Operational) 40 C to +125 C 26V Electrical Characteristics V IN = 10V, V O = 3V, I O = 1A, C O = 47 µf, R1 = 2.7k, T J = 25 C, unless otherwise specified. Boldface limits apply over the entire operating junction temperature range. Parameter Conditions Typical Min Max Units (Note 4) Reference Voltage 5 ma I O 1A V 5mA I O 1A, V V O 1V V IN 26V Output Voltage 2 3 V Range V IN = 26V V Line Regulation I O = 5 ma, V O 1V V IN 26V %/V Load Regulation 50 ma I O 1A % Dropout Voltage I O = 0.1A, V O 100 mv V 0.3 I O = 1A, V O 100 mv V 1 Quiescent Current I O 1A ma Dropout Quiescent V IN = V O,I O 1A ma Current Ripple Rejection V ripple = 1 Vrms, f ripple = 1 khz, db I O = 5mA Output Noise 10 Hz 100 khz, I O = 5 ma µv ON /OFF Input (V OUT : ON) V Voltage (V OUT : OFF) ON /OFF Input V ON/OFF = 0.8V (V OUT : ON) µa Current V ON/OFF = 2.4V (V OUT : OFF) Output Leakage V IN = 26V, V ON/OFF = 2.4V µa Current V OUT = 0V Current Limit V OUT = 0V A Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the deivce is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: Human body model, 100 pf discharged through a 1.5 kω resistor. Note 3: The maximum power dissipation is a function of T Jmax, θ JA and T A. The maximum allowable power dissipation at any ambient temperature is P D = (T Jmax T A )/θ JA. If this dissipation is exceeded, the die temperature will rise above 125 C and the LM2991 will go into thermal shutdown. For the LM2991, the junction-to-ambient thermal resistance is 53 C/W for the TO-220, 73 C/W for the TO-263, and junction-to-case thermal resistance is 3 C. If the TO-263 package is used, the thermal resistance can be reduced by increasing the PC board copper area thermally connected to the package. Using 0.5 square inches of copper area, θ JA is 50 C/W; with 1 square inch of copper area, θ JA is 37 C/W; and with 1.6 or more square inches of copper area, θ JA is 32 C/W. Note 4: Typicals are at T J = 25 C and represent the most likely parametric norm. 3

4 Typical Performance Characteristics Dropout Voltage Normalized Output Voltage Output Voltage DS DS DS Output Noise Voltage Quiescent Current Maximum Output Current DS DS DS Line Transient Response Load Transient Response Maximum Output Current DS DS DS Ripple Rejection Output Impedance ON /OFF Control Voltage DS DS DS

5 Typical Performance Characteristics (Continued) Adjust Pin Current Low Voltage Behavior Maximum Power Dissipation (TO-220) DS DS DS Maximum Power Dissipation (TO-263) (See Note 3) DS Application Hints EXTERNAL CAPACITORS The LM2991 regulator requires an output capacitor to maintain stability. The capacitor must be at least 10 µf aluminum electrolytic or 1 µf solid tantalum. The output capacitor s ESR must be less than 10Ω, or the zero added to the regulator frequency response by the ESR could reduce the phase margin, creating oscillations. The shaded area in the Output Capacitor ESR graph indicates the recommended ESR range. An input capacitor, of at least 1 µf solid tantalum or 10 µf aluminum electrolytic, is also needed if the regulator is situated more than 6 inches from the input power supply filter. Output Capacitor ESR Range DS MINIMUM LOAD A minimum load current of 500 µa is required for proper operation. The external resistor divider can provide the minimum load, with the resistor from the adjust pin to ground set to 2.4 kω. SETTING THE OUTPUT VOLTAGE The output voltage of the LM2991 is set externally by a resistor divider using the following equation: V OUT = V REF x(1+r 2 /R 1 ) (I ADJ xr 2 ) where V REF = 1.21V. The output voltage can be programmed within the range of 3V to 24V, typically an even 5

6 Application Hints (Continued) greater range of 2V to 25V. The adjust pin current is about 60 na, causing a slight error in the output voltage. However, using resistors lower than 100 kω makes the adjust pin current negligible. For example, neglecting the adjust pin current, and setting R2 to 100 kω and V OUT to 5V, results in an output voltage error of only 0.16%. ON/OFF PIN The LM2991 regulator can be turned off by applying a TTL or CMOS level high signal to the ON/OFF pin (see Adjustable Current Sink Application). Typical Applications FORCING THE OUTPUT POSITIVE Due to an internal clamp circuit, the LM2991 can withstand positive voltages on its output. If the voltage source pulling the output positive is DC, the current must be limited to 1.5A. A current over 1.5A fed back into the LM2991 could damage the device. The LM2991 output can also withstand fast positive voltage transients up to 26V, without any current limiting of the source. However, if the transients have a duration of over 1 ms, the output should be clamped with a Schottky diode to ground. Fully Isolated Post-Switcher Regulator DS Adjustable Current Sink DS

7 Equivalent Schematic DS

8 Physical Dimensions inches (millimeters) unless otherwise noted 5-Lead T0-220, Straight Leads (T) Order Number LM2991T NS Package Number T05A 5-Lead T0-220, Bent, Staggered Leads (T) Order Number LM2991T Flow LBO3 NS Package Number T05D 8

9 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) TO Lead Plastic Surface Mount Package Ordering Number LM2991S NS Package Number TS5B 9

10 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 16-Lead Ceramic Dual-in-Line Package Order Number LM2991J-QMLV VEA Order Number LM2991J-QML QEA NS Package Number J16A 10

11 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 16-Lead Ceramic Surface-Mount Package Order Number LM2991WG-QML QXA NS Package Number WG16A LM2991 Negative Low Dropout Adjustable Regulator LIFE SUPPORT POLICY NATIONAL S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. National Semiconductor Corporation Americas Tel: Fax: support@nsc.com National Semiconductor Europe Fax: +49 (0) europe.support@nsc.com Deutsch Tel: +49 (0) English Tel: +49 (0) Français Tel: +49 (0) Italiano Tel: +49 (0) National Semiconductor Asia Pacific Customer Response Group Tel: Fax: sea.support@nsc.com National Semiconductor Japan Ltd. Tel: Fax: National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

LM2991 Negative Low Dropout Adjustable Regulator

LM2991 Negative Low Dropout Adjustable Regulator General Description The LM2991 is a low dropout adjustable negative regulator with a output voltage range between b2v to b25v The LM2991 provides up to